(a) Technical Field
The present disclosure relates to a method of controlling an engine speed of a hybrid vehicle. More particularly, the present disclosure relates to a method of controlling an engine speed of a hybrid vehicle that improves fuel consumption and starting responsiveness of the hybrid vehicle by maximizing an output of a hybrid starter-generator (HSG) due to differentiating an output area of the HSG according to a battery voltage, and by minimizing a vibration due to controlling a speed of the HSG having an increased output even while raising a speed of an engine using a flywheel having reduced inertia.
(b) Description of the Related Art
A hybrid vehicle is a vehicle using two or more different kinds of power sources and is generally driven by an engine that obtains a driving torque by burning fuel and by a motor that obtains a driving torque with battery power. A hybrid vehicle may be formed according to various configurations, such as using an engine and an electric motor as a power source, while a Transmission Mounted Electric Device (TMED)-type hybrid vehicle includes a motor attached to a transmission. The TMED-type hybrid vehicle may include an engine clutch inserted between the transmission and the engine so as to implement an electric vehicle (EV) mode and a hybrid electric vehicle (HEV) mode using disconnection and connection of the engine clutch. Further, a TMED-type hybrid vehicle has an intrinsic characteristic according to each production company, and some hybrid vehicles have a hybrid starter-generator (HSG) that is connected to an engine by a belt. The HSG charges a battery by operating as a generator when starting an engine or in a state in which an engine is started.
When a hybrid vehicle having an HSG is converted from an EV mode to an HEV mode, by separating starting and driving using a driving motor and the HSG, starting responsiveness can be secured and vibration can be minimized. However, because a conventional HSG use area is selected in consideration of unfavorable conditions amidst running of a vehicle, an output of the HSG is limited. However, because a vehicle is mostly run in a general driving condition, it is necessary to variably use an HSG output torque according to an available voltage of a battery.
With respect to the engine, in order to reduce vibration and rotation vibration (e.g., by a reciprocal motion of a piston), a flywheel can be provided. The engine generates inertia by a rotation motion, and about 65-70% of inertia is caused by the flywheel. Inertia acts in an opposite direction of a moving direction, and when inertia is large, if an engine rotates, damage increases. Therefore, while a vehicle is running, in order to minimize an engine output loss due to inertia resistance, it is necessary to reduce inertia of a flywheel. However, because the flywheel reduces an engine vibration, when simply reducing inertia of the flywheel only, a driver may experience displeasure due to a vibration.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore it may contain information that does not form the related art that is already known in this country to a person of ordinary skill in the art.